Could rain actually help our flooding woes?

In the short-term, we've got more cold and snow on the way. However there's something more important in the long-term: rain! Before we go and make a big deal out of our flooding potential, let's think about how this rain may be a blessing in disguise.

When you have ice-jam flooding FIGURE 1, the only way to get it to go away is to melt it off. That's plain and simple. What's more complicated when you melt it off by way of rain we have to keep the amounts light and the duration fairly long.

Solution #1: If Monday's rainfall is light (under 1/2 inch) and it occurs over the course of many hours the rain will melt the icecover right into the river. FIGURE 2

Problem #1: If the rain doesn't stop and an inch or two fall, additional flooding will be induced (but mainly occur in areas that are not protected by (or upstream of) dams). FIGURE 3

Problem #2: There is a chance that the ice that's there is too thick and too compressed to melt fast enough. Should that be the case, the rain would produce runoff that would flow directly on top of the ice itself! This would be the worst-case scenario because areas that are flooded now would be inundated by additional water flows.

I spoke with Jim Allsopp, Warning Coordination Meteorologist at the National Weather Service in Romeoville this afternoon. He agreed that Monday's rain could be just what we need so long as it doesn't come down too hard.

Could rainfall actually stop a flood? We'll have to wait and see next week. For the latest on our forecast amounts and duration, keep tabs on the blog. -ERIC